A liquid crystal display (hereinafter, referred to as “LCD”) device is an electronic device changing and conveying various electric information generated from various apparatuses to visual information by using change of transmittance of liquid crystals according to an applied voltage.
The LCD device is a device displaying information, but has no self-light emitting source. Thus, the LCD device needs a separate device in the backside in order to brighten the whole screen of the LCD device uniformly. The device providing a light is a backlight unit.
According to the installation method of cold cathode fluorescent lamp (hereinafter, referred to as “CCFL”), the BLU may be made in two methods: a direct-light method in which a lamp is located under an LCD panel, and an edge-light method in which a lamp is disposed on the side of a light guide plate.
FIG. 1 is a cross-cross-sectional view illustrating a conventional backlight unit of a LCD device.
Referring to FIG. 1, the backlight unit is driven by the edge-light method, and comprises a light source unit 110, a light guide plate 120, a reflection sheet 130, and an optical film 140.
The light source unit 110 comprises at least one light source 112 and a light source reflection plate 114.
The light source 112 generates a light having a predetermined wavelength.
The light generated from the light source 112 is reflected by the light source reflection plate 114 and the reflection sheet 130. Then, as shown in FIG. 1, the reflecting light is diffused uniformly through the light guide plate 120.
The optical film 140 comprises a diffusion sheet 142, a prism sheet 144 and a protection sheet 146.
The light which is diffused uniformly in the light guide plate 120 passes through the diffusion sheet 142. The diffusion sheet 142 diffuses or concentrates the light passed through the light guide plate 120, thereby making luminance uniformly, and widening the viewing angle of the LCD.
The luminance of light passed through the diffusion sheet 142 is decreased rapidly. To prevent it, a prism sheet 144 is used. The prism sheet 144 refracts the light emitted from the diffusion sheet 142 in a low angle to collimate the light toward the front direction so that the luminance is improved within the effective viewing angle.
The protection sheet 146 is disposed on the prism sheet 144, and prevents the prism sheet 144 from scratch, and widens the viewing angle narrowed by the prism sheet 144.